1. Field of the Invention
The present invention relates to an electric rotary machine (hereinafter referred to as “rotary machine,” or occasionally “motor” as appropriate), and more particularly to a radial gap type rotary machine comprising an armature with discrete salient poles.
2. Description of the Related Art
In a conventional rotary machine including a stator armature (hereinafter referred to as “armature”) structured such that a plurality of ring-shaped yoke pieces, which are made of a soft magnetic plate, such as a silicon steel plate, and which each have a plurality of pole tooth portions protruding radially, are stacked in the axial direction, since each of the ring-shaped yoke pieces is punched out integrally with the plurality of pole tooth portions as a single piece (the armature composed of the ring-shaped yoke pieces thus structured is hereinafter referred to as “integral armature” as appropriate), pole teeth each composed of a stack number of pole tooth portions are not partitioned structurally and therefore a resultant armature will have superior magnetic efficiency (low reluctance). However, in a small rotary machine, since a wire is usually wound directly on each of the pole teeth, the integral armature makes the winding operation troublesome, and makes it extremely troublesome when the rotary machine is of inner rotor type. As a result, the winding operation takes a long time, and the winding incurs unsatisfactory space factor as well. And, due to the flyer-winding involved in this case, the wire is subject to torsional stress during the winding operation, thereby failing to ensure reliability of the winding area.
Under the circumstances above described, a rare earth magnet having high energy product has been developed recently, and the structure of a rotary machine can be reviewed by means of magnetic circuit analysis using a computer. This works to enable a rotary machine with an armature of discrete salient pole structure (this armature is hereinafter referred to as “discrete armature” as appropriate) to obtain requisite motor characteristics. The rotary machine with the discrete armature may give some undesired increase in reluctance but offers great advantages of easier winding operation and increased space factor of winding, which outweigh the disadvantageous increase in reluctance. From this, it is now realized that the rotary machine with the discrete armature produces higher performance and is manufactured less expensively on the whole, and there is a growing demand for the discrete armature.
One example of the discrete armature is manufactured such that pole tooth portions are dismembered off its main body portion of an integral armature, a wire is wound on each of the dismembered pole tooth portions thereby constituting each salient pole portion, and such that the pole tooth portions each with a wire wound thereon (namely, the salient pole portions) are rejoined to the main body portion by laser-welding, or the like.
The armature thus structured and manufactured, however, has a disadvantage that the integral armature has to be first sectioned into the main body portion and the pole tooth portions and later the sectioned portions have to be put back together, thereby requiring an additional time. Also, when the pole tooth portions each with a winding (salient poles) are rejoined to the main body portion, the stack layers of the both portions have to be matched with each other, and therefore it is required that respective portions be held together by a well-maintained tool and surely welded plate by plate for ensuring precision, which results in decreased workability. And, joints (welded portions) deteriorate significantly in mechanical strength and magnetic characteristics.
To overcome the above described problems, the present inventors disclosed in Japanese Patent Application Laid-open No. 2001-238377 a radial gap type rotary machine, in which an armature comprises: a plurality of discrete salient poles; a cylindrical pole tooth ring for positioning and magnetically and mechanically connecting the salient poles to one another; and a cylindrical stator ring adapted to house the salient poles and to decrease leakage flux resulting from magnetic discontinuity.
In the above described rotary machine, the salient poles must be accurately arranged as determined and securely fixed to achieve the performance required. If the salient poles are not accurately arranged as determined, the rotary machine suffers an increase in torque ripple and cogging torque, resulting in deteriorated performance. To solve this problem, in the conventional rotary machine, the salient poles are each provided with a bobbin, and are put together such that their respective bobbin flanges are firmly pressed side to side against one another or are configured so as to engage with one another, and then that a molding resin is injected to fill the space between the salient poles for further secure fixation.
The above mentioned solution, however, raises the following problem. When the molding resin injected is cured, pole teeth of the salient poles are moved slightly due to the stress resulting from the contraction of the resin, which generates variance in contact condition between respective pole teeth and the stator ring thereby increasing torque ripple and cogging torque. Also, the movement of the pole teeth may cause the stator and the rotor to fail to stay concentric with each other, thereby giving a similar problem. Especially, a larger-size rotary machine is larger in the amount of the resin injected, rendering the problem more noticeable.